Если погода испортится, мы быстро уберём вещи под навес и сядем в машину.

This is a very common point of confusion.

In Russian, after если for a real future condition, you often use a perfective verb form that looks like present tense, but because perfective verbs do not have a true present tense, it actually refers to the future.

So:

• если погода испортится = if the weather gets bad / if the weather turns bad

Here испортится is perfective, so it focuses on the moment of change.

Compare:

• если погода портится = if the weather is getting worse / gets bad in a more general or habitual sense
• если погода испортится = if the weather does become bad on this specific occasion

So this structure is completely normal Russian.

The base verb is:

• испортить = to spoil / ruin something

For example:

• испортить план
• испортить еду

With -ся, it becomes:

• испортиться = to become spoiled / to go bad / to get ruined

So:

• погода испортится does not mean someone will spoil the weather
• it means the weather will turn bad

In other words:

• испортить = transitive, affects an object
• испортиться = intransitive, something itself changes for the worse

The -ся here is not really a direct equivalent of English self. It is just part of how Russian forms many intransitive or change-of-state verbs.

Both are 1st person plural forms, matching мы.

• уберём comes from убрать
• сядем comes from сесть

They are both perfective verbs, so their future is formed as a simple future, not with будем.

So:

• мы уберём = we will put away / move / remove
• мы сядем = we will sit down / get in

This is different from imperfective verbs, which form the future with буду / будешь / будет etc.

For example:

• мы будем убирать = we will be putting away / we will be cleaning up
• мы будем садиться = usually a repeated or process-oriented idea, not natural here

Because the sentence describes quick, single, completed actions in response to the weather changing, perfective verbs are the natural choice.

Убрать is a very flexible verb, and that is why learners often ask about it.

Depending on context, убрать can mean:

• put away
• remove
• tidy up
• move out of the way

In this sentence, уберём вещи под навес most naturally means something like:

• move the things under shelter
• put the things away under the shelter
• get the things under cover

So it is not necessarily about neatness or cleaning. It is about moving the items to a protected place.

Because вещи is the direct object of уберём, so it is in the accusative plural.

The noun is:

• вещь = thing
• nominative plural: вещи
• accusative plural: вещи

For inanimate plural nouns, the accusative usually looks the same as the nominative. That is why the form does not change.

Compare:

• мы уберём вещи = inanimate, accusative looks like nominative
• мы увидим друзей = animate, accusative plural matches genitive

So вещи is accusative here, even though it looks identical to the nominative plural.

Because под can take different cases depending on whether there is movement or location.

Here there is movement:

• уберём вещи под навес = we’ll move the things under the shelter

So Russian uses accusative:

• под навес

If the things were already there and you were only describing their location, you would use instrumental:

• вещи лежат под навесом = the things are lying under the shelter

So the contrast is:

• куда? where to? movement → под навес
• где? where? location → под навесом

Yes, сесть basically means to sit down, but with vehicles it is very commonly used in the sense of get into and seat yourself.

So:

• сесть в машину = to get into the car
• сесть в поезд = to get on the train
• сесть в автобус = to get on the bus

Russian often focuses on the act of entering and taking a seat, where English might more naturally say get in or get into.

So in this sentence, сядем в машину is a normal way to say we’ll get into the car.

This is the same movement-vs-location pattern as with под навес.

With в:

• в + accusative = motion into
• в + prepositional = location in

So:

• сядем в машину = we’ll get into the car → motion
• мы уже сидим в машине = we are already sitting in the car → location

That is why the sentence uses в машину.

Yes. Russian can say:

• Если погода испортится, то мы быстро уберём вещи под навес и сядем в машину.

The то is optional here.

Without то, the sentence is completely normal and very natural.
With то, the structure can feel a bit more explicit or slightly more emphatic:

• if X happens, then we will do Y

In everyday Russian, leaving out то is very common.

Russian word order is flexible, but not random.

Here:

• мы быстро уберём вещи под навес и сядем в машину

is a very natural neutral order.

Why this works well:

• мы = subject
• быстро comes before the verb it most naturally modifies
• уберём вещи keeps verb + object together
• под навес shows where the things will be moved
• и сядем в машину adds the second action

You can move words around for emphasis, but the nuance changes. For example:

• Если погода испортится, быстро мы уберём вещи... sounds marked or unnatural in ordinary speech
• Если погода испортится, мы уберём вещи под навес быстро... is possible, but less neutral

So the given order is a good standard pattern.

Yes.

Если погода испортится is a subordinate clause, and мы быстро уберём вещи под навес и сядем в машину is the main clause. Russian separates them with a comma.

So:

• Если погода испортится, мы быстро уберём вещи под навес и сядем в машину.

That comma is required in standard writing.

If the clause comes second, you still use a comma:

• Мы быстро уберём вещи под навес и сядем в машину, если погода испортится.